During certain operating conditions of a motor vehicle, it may be desirable to temporarily reduce the load on an internal combustion engine powering the vehicle. For example, load reduction may be desired to increase power delivered to a drive train during engine startup, vehicle acceleration, brake vacuum replenishment, and stall mitigation. Various vehicle components may be powered by engine rotation via physical coupling to the engine. As these components require torque to be driven, they impose loads on the engine. Accordingly, reduction of engine load may be achieved by reducing the torque required to drive such components.
One such component that may be coupled to and driven by the engine is a compressor of an air conditioning system configured to enable climate control in a vehicle cabin. The automotive context in which the air conditioning system is placed, however, presents a number of challenges for ensuring desired operation of the air conditioning system. The air conditioning system is configured to generate a required flow of coolant and compress the coolant to increase its temperature so that heat may be exchanged during a condensing cycle; these requirements must be met over a wide range of compressor speeds and are dependent upon ambient conditions. Further, compressor operation is constrained by noise, vibration, and harshness (NVH) and reliability requirements during its service life.
In some approaches, the torque required to drive an air conditioning system compressor is reduced by regulating a current supplied to a control valve of the compressor. Specifically, the current is set to a minimum value (e.g., 0 A) for short periods of time to reduce the amount of circulated coolant in the air conditioning system and regulate the oil return to the compressor.
The inventors herein have recognized several issues with this approach. In particular, the control valve current is pulsed between the minimum valve and a maximum value, which does not reduce the net load on the engine. Moreover, NVH and reliability requirements restrict the control valve current to a limited range (e.g., between 0.25 and 0.85 A). The extent to which the torque delivered to the compressor is this limited by the lower end of this current range.
One approach that at least partially addresses the above issues includes a method of controlling a compressor, comprising regulating a discharge capacity of the compressor via a control current supplied to a control device, holding the control current supplied to the control device at substantially zero amperes for a first duration, and stepping the control current from substantially zero amperes to a sustainable current that provides a sustainable level of a performance parameter of the compressor.
In a more specific example, the method further comprises ramping the control current up to an operational current over a second predetermined duration from the sustainable current.
In another aspect of the example, the performance parameter relates to noise, vibration, and/or reliability of the compressor.
In yet another aspect of the example, the compressor is an externally variable discharge compressor.
In still further another aspect of the example, the control device is a solenoid valve.
In this way, the load imposed on an engine may be reduced by reducing the torque required to drive a compressor coupled to the engine, in turn increasing the power available to a powertrain coupled to the engine. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.